The goal of this proposed research is to utilize the unique advantages of multiphoton fluorescence excitation and nonlinear scattering to develop methods for in vivo detection of cancer and in vivo studies in cancer biology. The proposed research and development consists of two concurrent research components; the first involves the application of multiphoton microscopy to well-defined transgenic mouse models of cancer to examine cancer progression and the potential for early detection. The second focus is on instrumentation development for gleaning the most information from tissue emission and on the engineering required to build an in vivo multiphoton endoscope, initially for multiphoton spectroscopy and then as required for multiphoton microscopy. To accommodate the breath of this application, there are four laboratories involved whose combined expertise encompasses all of the science and technologies required to successfully complete the project. The leadership will be centered at the NIH Developmental Resource for Biophysical Imaging and Opto-electronics (DRBIO). The 5 specific aims are: 1) A direct comparison of multiphoton imaging of intrinsic tissue signals with standard histological techniques, focusing on the discovery of new diagnostic criteria. 2) Testing the hypothesis that by using in vivo multiphoton microscopy, malignant cells can be traced from the time of mutancy initiation until appearance of the morphologically identifiable phenotype. 3) The development of detection instrumentation specifically optimized for the in vivo multiphoton microscopy proposed in Aims 1 and 2 and for the prototype multiphoton endoscopes defined in Aims 4 and 5. 4) Construction of a fiber endoscope for point or multiple point (fiber bundle) spectroscopy that uses multiphoton excitation in the near infrared and obtains spectral and fluorescence lifetime information from tissue. 5) Construction of a prototype raster-scanning fiber endoscope for multiphoton emission imaging in tissue. The ultimate objective of this program is to develop the strategy and determine the information infrastructure for noninvasive, microscopic medical detection and diagnosis of premalignancy and cancer.